Rotary fluid-meter



(ModeL) 8 SheetsS'heet I.

J. A. TILDEN.

. ROTARY FLUID METER. I

N0.- 324,-503.-- Patented Aug. 18, 1885.

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ROTARYFLUID METER.

Patented Aug. 18, 1885.

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(ModeL) 8 Sheets-Sheet 3.

J. A.VTILDEN. ROTARY FLUID METER. No. 324,503. I Patented Aug. 18. 1885.

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J. A. TILDEN.

ROTARY FLUID METER.

No. 324,503. Patented Aug. 18, 1885.

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J. A. TILDEN.

ROTARY FLUID METER.

No. 324,503. Patented Aug. 18, 1885.

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J. A. TILDEN.

ROTARY FLUID METER.

No. 324,503. Patented Aug. 18, 1885.

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ROTARY FLUID METER- No. 324,503. Patented Aug. 18, 1885.

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N. PETERSv FhmwLithngI-apher. Wnhingfion, D, C.

UNITED STATES PATENT @rrrcs.

JAMES A. TILDEN, OF HYDE PARK, ASSIGNOR TO HERSEY BROTHERS, or

BOSTON, MASSACHUSETTS.

ROTARY FLUID-METER.

SPECIFICATION forming part of Letters Patent No. 324,503,'dated August18, 1885.

Application filed December 22, 1884.

T all whom it may concern.-

Be it known that I, JAMES A. TILDEN, of Hyde Park, in the county ofNorfolk and State of Massachusetts,a citizen of the United States, haveinvented a new and useful Improvement in Fluid-Meters, of which thefollowing is a full, clear, and exact description, reference being hadto the accompanying drawings, forming a part of this specification [0 inexplaining its nature.

It is well known that a fluid-meter to be commercially successful mustbe capable of perfectly measuring or indicating the quantity of fluidwhich passes through it, regardless of the size of the stream, itsspeed, head, or any other condition. that it must not easily get out ofrepair, that its construction 'must be simple,and its manufactureinexpensive, and various meters have been made with some if notall ofthese conditions, but, so far as I am aware,there is not at present inthe market any meter which combines all of these features with certainnecessary wearing qualities to such an extent that it may be said to bea really commercially successful or practical meter; and while myinvention may not be perfect in every respect, yet it has all therequisites of an efficient, desirable,and cheap meter. t

The principle upon which the meter is constructed is so simple that butvery few parts or pieces are necessary and very little machineworkrequired in fitting them, and these can be placed in such very smallcompass that the weight of metal necessary for the casing is very small.7

The invention comprises, broadly speaking, a chamber having inlet andexhaust ports, and a piston for opening and closing 0 the exhaust-ports.The meter can hardly be called a rotary meter, because the piston doesnot rotate, and yet it is quite unlikein appearance any of the ordinaryreciprocatingpiston meters; but it combines, it may be 5 said, portionsof both systems in substantially this manner. The measuring-chamber ofthe meter is divided or separated upon its outer edge into measuringspaces or recesses, all of which open into the central portion of thechamber, but which may or may not be of uniform size and shape. Each ofthese spaces (Model.)

has its individual inlet and exhaust ports. The part which I call thepiston has a radially-ex'tending portion or lobe, which enters eachmeasuring space or recess and does not at any time leave it, and has amovement therein that causes it to be brought into contact with one sideof each recess near the mouth and to advance along the side continuouslyuntil it reaches the other side of the recess, when it returns acrossthe mouth of the recess or space to its original position. This movementof each lobe in each space or .rccess alternately exposes and closes theexhaust-ports, thereby preventing the flow of liquid from the cham- 6her only after it has entered what may be termed the measuring anddischarging spaces or recesses. The sides of the chamher and the sidesof the piston should be parallel when the piston is centrally located inthe chamber.

To understand the working of the device, it must be borne in mind thatthe liquid has free access to the chamber-that is, its inlet ports arenever entirely closedthat because 7 5 of the shape of the wall of thechamber and of the piston, the piston is kept in contact .with the wallof the chamber at a number of what I call contact points orlines, whichform in the measuring and discharging passages spaces or recesses. Thenumber of lines of contact depend, of course, upon the number of spacesor recesses. This separation or division of the chamber is necessary,because a full head is maintained in the larger part of the cham- 8 5her, and it is of course necessary to divide the spaces or recesses orportions thereof which are successively emptied from those which arebeing successively filled by liquid under pressure. This division isaccomplished by contact of the piston with the wall of the chamber. Thelobes in connection with the pertions of the wall which constitute orform the spaces or recesses also act to separate the exhaust-ports fromthe inlet-ports, so that each 5 space or recess that is discharging isseparated from the portion of the space that is filling by twocontact-lines, one between the outer surface of the lobe and the wall ofthe recess and the other between the surface of the inward IOOprojection of the wall and the surface of the piston between the lobes.These lines of contact continually advance until the water has beenexpelled from each space or recess. While, however, this discharge fromeach space or recess is going on by the movement of the lobe, the spaceor recess is filling behind the lobe. Of course the number of spaces orrecesses which are discharging simultaneously depend upon the entirenumber of spaces or recesses which the chamber contains, and there maybe several recesses or spaces discharging and receiving at the sametime. This advancing movement of the lobe in each space or recess doesnot continue beyond its individual space, but upon reaching the end ofthat space or recess it returns across the mouth or entrance of itsrecess or space to its original position, while the piston as a whole,without revolving, moves on a circular path.

In the drawings, Figure 1 represents a side elevation of the machine.Fig. 2 is a plan view of a portion of the meter above the line a 00 ofFig. 1, inverted, showing the piston and upper series of exhaust'ports.Fig. 3 is a view, principally in vertical central section, showing,especially, the mechanism for connecting the piston with theregisteringtrain. Fig. 4 is a section upon the line 3 y of Fig. 3, alsoshowing the lower series of exhaust-ports and the inletports. Fig. 5 isa view, princi' pally in vertical section, upon the lines 2 z of Fig. 4,showing, especially, the relation of the exhaust-ports, meter-walls, andspaces or re cesses when discharging. Fig. 6 is a plan view of the packin g-piece between the base and main sections of the meter. Fig. 7 is aplan view of the base-section, showing the receiving-chamber and theinlet and outlet passages. Fig. 8 is a perspective view of the piston.Figs. 9 to 15, inclusive, illustrate special details of a modified formof construction. Figs. 16, 17, and 18 are diagrams showing that changesin the formand size of the chambers, spaces, and pistons do not vary theprinciple of the construction. Fig. 19 is a diagram showing bycalculation the differencesin pressure which cause the action of themeter. Figs. 20 and 21 are sections of the reducinggears hereinafterdescribed, and Fig. 22 is a view of the sleeve forming the support ofthe drum carrying the gears.

Preferably,the casing of the meter comprises three principal parts orsections-first, the basesection A; second, the body or main section B,and, third, the shell C, forming the chamber 0, containing theregistering mech anism.

The base-section is made somewhat larger in circumference than the mainsection, and the two parts are-fastened together by bolts a, which passthrough the flange b of the main section. The base-section has theinlet-pas sage a, which opens into the distributing-chamher a and theoutlet-passage a. The distributing-chambcr a occupies almost the entireupper portion of the base, and its object is to provide means for theready distribution of fluid simultaneously through the various inlet-ports to the main chamber 1).

Between the sectionsAB is apacking-ring, B, which is shaped as shown inFig. 6, and is provided with holes for the boltholes, the inlet-ports,and outlet-passage. Above this packing-ring is a metal plate, B, whichmay be called a port-plate. It rests upon the packing-ring B, and isheld or fastened in place upon it and the upper surface of section A,surrounding the chamber a and the central projection, a by the bolts (1,the plate being within the main section B and its edge proj ecting intoa recess formed in the under edge thereof. This port-plate has the holesE,wh ich form the inlet-ports to the chamberD and connect thedistributing-chamber a therewith. These ports E are arranged,preferably, to open into each space or recess (1 of the chamber D at oneside thereof. Theport-plate also has a central hole, which forms aportion of the outlet a and the escape or exhaust ports E,which arerecesses formed in the upper surface of the plate, and arranged toextend from one side of each recess or space (I inward upon converginglines. The chamber 1) has the measuring recesses or spaces d arrangedabout its outer edge, which open into the central portion, and theprojections or portions of the wall of the chamber which form spaces orrecesses I have lettered d. The piston F preferably is made of hardvulcanized ind1a-rubber, gutta-percha, or other equivalent material, andhas the wings or lobes f, which extend radially therefrom,and thecentral hole, f.

For the best working of the device it is desirable,but notessential,that the surface of the piston, when the same is centrallylocatcdin the chamber D, shall be parallel with the surface of thechamber, so that as the surface of the chamber is made up of alternatingrecesses and projections, so the surface of the pistons is made up ofalternating lobes and recesses. The central hole, f, of the piston formsa part of the exhaust or outlet passage, and is large enough to alwayspermit the escape of fluid therefrom into the outlet a, re gardless ofthe position of the piston.

In addition to the lower set of exhaust-ports, E, I have formed in theunder surface of the upper plate, D which forms the top of the mainsection B, another set of-exhaustports, E". (Shown in Fig. 2.) They areof thesaine shape and connect the same parts of the spaces or recesseswith the opening f as the lower exhaust-ports, E. There is also arrangedin the hole f a perforated disk, G, (see Figs. 2 and 3,) by which motionis communicated to the shaft which operates the train of gearscomprising the registering mechanism. This disk carries at its center astud, g, which projects downward from the drum 9, which is pivoted at gto the screw sleeve 5 which passes through the hole in the plate I), andislocked thereto by the nut which screws upon the thread and themovement of the piston causes the drum to be revolved upon the .sleevethat is, the-drum and stud form substantially a crank. It is necessary,however, as the chamber is of smallcapacity and as the motion ofthepiston is rapid, to reduce the motion of the piston verycons'iderably,and it is desirable to do so in as simple a manner and with as few partsas possible, in order that the construction maybe cheap and as littleweight of metal used as possible; and I employ for this purpose a trainof four gears, one of which, 9 is stationary, being secured to the endof the sleeve 9 The gears g g are attached to the drum by the shaft orpinion g, to which they are keyed, and the gear 9 meshes with the gearThe gear 9 is arranged to mesh with the fourth gear, g,which is keyed orfastened to the spindle gt, which communicates motion to theregistering-train. As the drum revolves about the sleeve g ,it isobvious that if the gear 9 has more or less teeth than the gear 9 itwill be caused to move each revolu- V tion of the drum a certain portionof a revolution depending upon the difference in the number of teethbetween the two gears. Itis also obvious that if the gears g havethesame number of teeth as the gear 9 a movement of rotation will becommunicated to the shafts or spindle 9*. further reduce or change therate of the rotation of the shaft 9 then the gear 9 may have more orless teeth than the gear 9 as the case may be, as also may the gear g,-and in the drawings I have represented. the gear g as provided with tenteeth, the gear 9 with nine teeth, the gear 9 with eight teeth, the gearg with nine teeth, so that upon every complete revolution of the drumthe shaft 9 is moved one eighty-first of a revolution, and it thereforerequires eighty revolutions of the drum to make one complete revolutionof the, shaft, the spindle or shaft 9" being used, of course, to operateany registering mechanism.

It will be seen by this construction of gearing that the drum carryingthe gears g g revolves from left to right,and that the gear wheels 9 gbeing carried by the drum, are

caused by the meshing of the gear 9 with the stationary gear 9 to turnfrom right to left, and that the meshing of the gear as it is turnedupon its revolution about the gear 9"",

causes the gear to be moved, as above specified, one eighty-first of arevolution for each revolution of the drum and the gearsg 9 about it.

In operation the liquid passes into the distribution-chamber a and.through the inletports E into the chamber D,moving the piston toward oneside of the chamber'and causing the formation of measuring ordischargespaces by the contact of the various portions of the piston with thechamber-wall. This position of the piston is well shown in Fig.4, wherethere have been formed six divisions of the three spaces or recesses dby the contacting of the piston at the points 1, 2, 3, 4, 5, 6, and 7,and of these three recesses or spaces, twonamely, the small spacesmarked M and the If it is desired to still Y space Mare connected by thedischargeports E E with the escape-passage, while the space M is aboutto be; but the fluid, upon being admitted to the chamber under pressure,not only immediately moves the piston to the position shown in Fig. 4,which is one ofany number of positions which it might cause it toassume, and from such position it causes it to advance or move, so thatthe lobes which are in contact with the wall of thechamber, arecaused tocontinue that contact until they have expelled all the fluid which is inthe discharge spaces or recesses before them, when each lobe insuccession will leave the surface and return upon an'arc of a circle toa position where it again comes in contact with the surface of the wallof the chamber on the opposite side fromthat which it left, and againadvances and expels the fluid from its recess or space.

It will be seen that each recess or space becomes in succession adischarge space or recess, and that as soon as the piston has movedsufficiently to uncover the inner end of its escape-ports it begins todischarge through such ports into the escape-passages b a and that whilea portion of each space or recess is discharging another portion is alsoreceiving the liquid under pressure through the ports E.

To illustrate why with the arrangement of the inlet and exhaust-portsdescribed the piston is compelled to make the motion that it does, Ihave shown in Fig. 19 by'diagrams thedifferences in pressure upon bothsides of the piston and theextent of the surface which is subjected tothe direct pressure of the entering fluid.

It is obvious that the chamber D, excepting the spaces which aredischarging, is filled with fluid under pressure, and that the pressurefor moving the pistons is that which enters each space or recess whichis being discharged, and behind'the respective discharging lobe. Forinstance, referring to Fig. 4, the piston is receiving motion from thefluid which enters the spaces through the ports marked N N N, but fromno other. It is not necessary that the main chamber and piston be shapedas represented in Fig. 4, for I have ascertained that the piston mayhave any number of lobes and recesses, from three upward, and that theymay be of any size and of different sizes for the same piston, the onlydifference to be observed being that the piston and chamber: wall mustbe so shaped as to provide the contact-lines in the surface of thepiston or chamber-wall, whereby the formation of measuring chambers iseffected.

In Fig. 16 I have illustrated a piston having three lobes in a chamberhaving three measuring and discharge spaces or recesses. In Fig. 17 Ihave shown a piston with two large lobes and two small ones, and achamber with corresponding recesses or spaces. In Fig. 18 I haverepresented the piston as having square lobes, and the chamber withspaces which substantially follow the shape of the lobes, the

only variation being that they are rounded at the corners.

It will be obvious from what I have stated that the meter is very simplein construction, that it has but very few parts, which require butlittle machine-work and are easily fitted and put together, and it isalso apparent that a substantial ly-pcrfect registration of the] iquidwhich passes through the meter is obtained, as it all is obliged to passinto the measuringspaces, which are successively emptied. It will, beseen, further, that this measuring of the liquid takes place veryrapidly, and with comparatively very little friction of the wearingparts, and that the construction of the piston and chamber is such thatsediment cannot interfere with the proper working of the invention, andthat wear, up to a certain extent, improves the efficiency of the meterin that it causes the contacting surfaces of the piston and chamber tofit themselves as they wear.

To still further cheapen the manufacture I show in Figs. 9 to 15,inclusive, a construction which enables me to use, instead of thecomparatively expensive easing of composition, an iron casing. This Iaccomplish by making the base-section entirely of iron, employing twocomposition port-plates, O O, the plate 0 being like that described, andthe plate 0 having simply the exhaust-passages E". The piston is made ofhard rubber, gutta-percha, or other like non-corrosive material, and thewall 0 (see Fig. 14) of the chamber D is 3 formed of a ring or sleeve ofgutta-pereha,

hard india-rubber, or even of composition, which is fitted into the ironshell or easing of the main section. This non-corrosive movable wall ofthe chamber is fastened to the casing by means of a key, 0,which entersa groove in the ring and a corresponding one in the inner surface of theiron shell, or in any other suitable way. A view in perspective of themovable wall is shown in Fig. 14.

It will be seen that by this construction not only can an iron shell beemployed, but that the principal wearing parts--name1y, theportplatcs,the piston,and the wall of the chambermay be easily removedand others substituted therefor. The port plates are also held in placeby suitable keys or in any other desirable way, and it will be observedthat they extend upon the two end surfaces of the removable wall. (SeeFig. 9.)

Of course the invention can be utilized as a pump or motor, if desired.

It will be observed that by making the mechanism for reducing themovement of the pis' ton in compact form, I am enabled to place it inthe n1casuring-chamber and within the hole formed in the piston, therebyeconomizing space.

As the gears are inclosed in a drum or casing, no sediment can reachthem to disturb their easy action.

\Vhile the invention as shown in the draw ings represents a pistonwhich, while not retatin g moves in a circular path, yet by changing theforms of the piston-lobes and the shape of the walls of the chamberthepiston may be made to take a square, rectangular, elliptical, or anyother shape, the conditions governing these various movements dependingentirely upon the shape of the surface of the piston, the surface of thewall of the chamber, and the relation which they bear to each other; butwhile these different movements may be given to the piston the principleof its action is not changed, as the lobe or portion of the piston whichpenetrates the measuring-space will have a continuous movement in saidspace, whether its path be circular, square, rectan' gular, elliptical,or of any other shape.

It will be seen that the contacting points or lines of the piston orvalve are, in the opera tion of dividing the chamber intomeasuringspaces or recesses and discharging the same, always upon theone side of the piston, and that these contacting points are broughtsuccessively into operation, not by the rotation of the piston or valve,but by their successive reverse 1novements,so that the piston or valve,while appearing more like a rotating piston or valve, is in principlemore like a reciproeating piston or valve, in that each of its lobes orprojections is caused to enter ameasuring space or recess, advancetherein, empty it, and return to its original position to again advancein the said space or recess and empty. In making this movement thecontact between each lobe and the wall is not maintained during thereverse movement of each lobe or projection.

,It will further be seen that by this construction the contacting pointsalways being upon one side of the piston, and the piston being heldagainst the wall of the chamber by the water-pressure behind, or thatnot included within the contact-lines, it is very loosely fitted withinthe chamber, so loosely, indeed, that it is free to be moved back andforward therein the depth of a measuring space or chamber, and isdependent upon the water pressure for maintaining the proper contactwith the walls of the chamber and for its operation.

It will further be seen that from this priueiple of construction therecan be. very little friction between the running parts, and thatsediment or foreign substances cannot interfere with the fine andregular working of the device.

It will also be noticed that the piston in other respects has more ofthe principle of a reciprocating piston than of arotating piston, inthat each lobe or projection operates as a separate or distinct pistonor discharging device in connection with its respective space or recess,so that the recess or space being filled with liquid, the lobe enters itand presses the liquid therefrom through the exhaust-port. In otherwords, each lobe or projection. does not act to displace the liquid fromthe spaces or recesses, but to discharge the liquid therefrom by anadvancing movement from one end of the chamber or recess to the other.

It will be seen that the piston is made to fit the piston-chamberloosely, and that the necessary contact between its contactingsurfacesand the wall of, the chamber is obtained and maintained by so arrangingthe contacting.

points and the admission of pressure to the chamber that there shallalways be a sufficient area of the piston exposed to the direct pressureto' cause it to overcome all resistance and to keep it in contact withthe wall of the chamber while it is being moved.

I have shown in Fig. 19 a diagram which illustrates this feature ofconstruction, giving for the form of piston and piston-chamber thereinshown, the area of the piston upon which the direct pressure is exerted,and the area upon which there is a resisting force; and it will seenfrom the calculations noted upon said drawing that there is always anexcess of pressure to' maintain the piston in op eration in workingposition. The said diagram and calculations also show how the rotativeeffect is obtained.

In order that this result may be obtained it is not only necessary thatthe piston be loosely fitted, but that its surface should besubstantially parallel with the surface of the piston chamber. It willalso be seen'that by forcing the piston against the wall of the chamberby excess-0f pressure from behind, instead of drawing it to the wall'ofthe chamber by a crank or other rigid mechanical device, a substantiallyperfect contact must always ensue and continue, and that the piston isconstantly fitted to the wall of the chamber as it wears, the veryaction of wearing tending to give it a better fit, while if a crank orrigid connection be employed there is no compensation for wear oropportunity for it.

Another advantage which arises from this form of construction andoperation is that the meter is kept free from sediment, and theaccidental lodging of foreign matter on the piston lobes or walls of thechamber cannotiujure the meter or interfere with its practical working,as the lobe is pressed away by or rides over it, and it is thenimmediately washed off by the liquid.

It will also be observed that by making the 1 wearing portions of themeter separate or detachable from the casing, as shown in Figs. 9 to14., inclusive, the casing can be made of cast-iron, and the wearingparts of more expensive, durable, and non-corrosive material, therebylessening the cost of construction, increasing the efficiency and lifeof the meter, and enabling repairs to be cheaply, economically, andreadily made.

It will be observed that the reducing gearing and drum are contained ina recess within the piston, and that they are therefore within thepiston-chamber, and that by so arranging them less space is requiredthan where they are placed without the piston-chamber, as is generallythe case.

Having thus fully described my invention, I claim and desire to secureby Letters Patent of the United States- 1. In water meters, pumps, ormotors, apiston-chamber having the measuring spaces or recessesdescribed, each of which has a separate inlet-port and a separateoutlet-port directly connected therewith, as specified, in combinationwith a piston having alobe or projection entering each of said spaces orrecesses, and adapted to be brought in contact with the walls of thechamber by the excess of; pressure from behind, whereby the lobes aregiven the successive movements in their respective spaces or recessesindicated, all as set forth.

2. Ina water meter, pump, or motor, achamher having measuring recessesor spaces opening therefrom, in combination with a piston havingaseparate lobe or projection entering each of said recesses or spaces,and adapted to be brought in contact with the walls thereof, and to beheld in contact therewith during the movement of the piston by thedirect pressure exerted upon the piston, as specified, all substantiallyas set forth.

3. In Water meters, pumps, or motors, the combination of apiston-chamber having measuring spaces or recesses opening therefrom,each of which has an inlet-port and an outlet port, with a piston havinga lobe or projection entering each space or recess adapted to controlthe exhaust-port thereof and to maintain a contact with the wall of thespace or recess, which contact is maintained by the excess of directpressure in the piston-chamber, as described, all substantially assetforth.

4. In a water meter, motor, or pump, the piston-chamber having measuringrecesses or spaces forming a part thereof, a piston, F, having aprojection or lobe entering each of said spaces or recesses, whichprojections or lobes are adapted to be brought successively into contactwith the walls of said spaces or recesses, and to be moved therein, andthe con-- tact maintained during the discharge of the liquid from eachspace or recess by the direct pressure in the piston-chamber, asspecified, a register, and devices connecting the piston with theregister, all substantially as and for the purposes set forth.

5. In a water meter, motor, or pump, the piston-chamber having measuringspaces or recesses forming a part thereof, a distributing- IIO measuringrecesses or spaces d, the uncontrolled ports or passages E, connectingthe distributingchamber a with the recesses or spaces (1, theoutlet-ports E, and escape-pas sages connected therewith, and the pistonF, having the lobes or projections f, one for each of the measuringspaces or recesses d, and operated or moved therein to maintain contactduring the discharge of the liquid from each space or recess by thedirect pressure in the piston-chamber, as specified, all substantial] yas described.

7. In a water meter, motor, or pump, the independent or separatebascsection containing the inlet-passage a, the distributing-charm hera, and the outletpassage a, with the independent or separate sect-ion B,containing the piston-chamber D, with the measuring reccsses or spacesd, connected with the distributing chamber and outlet passage, asdescribed, and the piston F, having a lobe or projection for each ofsaid spaces or recesses, and the bolts for fastening the two sections ofthe meter together, all substantially as and for the purposes described.

8. The combination of the section A, having the distributiug-ehamber a",the section B, and the removable port-plate B having the ports E.

9. In a meter, motor, or pump, the combination of the section A, havingthe distributing-chamber a, the section B, containing themeasuring-chamber, the port-plate B", and the packing-ring B.

10. In a water-meter as a means for communicating the motion of thepiston to the register, the mechanism described, consisting of thestationary gear g, the revolving gears g 9 adapted to be revolved aroundthe stationary gear by the piston, and the gear 1/ upon theconnecting-spindle.

11. The combination of the piston F, the disk G, the drum or framepivoted, as described, to be revolved, and the differential gearsinclosed within said drum or case.

12. The combination, in a water-meter, of the piston-chamber D, thepiston F, the reducing mechanism or gearing for transmitting the motionof the piston to the registering device contained in a recess in thepiston, and the registering mechanism, all substantially as and for thepurposes described.

13. In a water meter, motor, or pump, a piston-chamber having measuringspaces or recesses, and a loosely-fitted piston having lobes orprojections extending into said spaces or recesses to form by contactwith the walls thereof successive discharge'spaces, the said walls beingshaped to provide the surface of the piston within the contacting linesof the discharge-spaces with less area than the remainder of the piston,subjected to the direct action of the pressure from behind, whereby thepiston or valve may be loosely fitted in the piston-chamber, and by theexcess of pressure caused by the difference in area is brought incontact with the walls of the meas uring spaces or recesses, maintainedin contact therewith, and rotated, all substantially as described.

JAMES A. TILDEN.

\Vitnesses:

F. F. RAYMOND, 2d, FRED. B. DOLAN.

